I. Field of the Invention
This invention relates generally to intravascular balloon catheters, and more particularly to a balloon catheter having a plurality of separately inflatable expander segments at a distal end thereof for positioning and deploying relatively large diameter stents.
II. Discussion of the Prior Art
It is known in the art to use a balloon catheter to deploy nonself-expanding stents as well as post extension of self-expanding stents within the vascular system. For the most part, stenting has been used in balloon and laser angioplasty procedures to provide reinforcement to a vessel wall. In such procedures, a compressed metal or plastic stent is positioned concentrically over a deflated expander member on the distal end of a catheter. The catheter is then introduced into the patient using the Seldinger technique and advanced through the vascular system until the expander member and stent are located at a desired site. By inflating the expander member, the stent is also expanded to a predetermined diameter determined by the O.D. of the inflated expander member. When the expander member is again deflated, the catheter can be withdrawn, leaving the expanded stent in place.
Those skilled in the art appreciate that as the diameter of the expander member increases, the burst strength of that expander member decreases. Thus, while a PET balloon of a 4 mm outside diameter can readily be inflated to 235 psi, larger diameter balloons, say 12 mm in diameter, may only be pressurized to about 100 psi without exceeding its burst strength.
A need exists for a balloon catheter capable of deploying relatively large diameter stents in peripheral blood vessels. As used herein, "peripheral" means any blood vessel external to the heart, including the aortic arch. For example, when attempting to treat abdominal aorta aneurisms (AAA), provision needs to be made for expanding a stent having a I.D. of about 12-40 mm depending on the sex and age of the patient. A balloon catheter having a single expander member of that size necessarily dictates that a lower pressure be used to avoid exceeding the burst pressure of the expander member. Thus, the lower pressure may be insufficient to expand the stent that is to be used in treating the AAA condition.
Another drawback of existing large diameter balloons, especially those fabricated from PET is their tendency towards "winging". When such a balloon is inflated and subsequently deflated prior to withdrawing the catheter, the deflated balloon tends to collapse in a form exhibiting flat wing-like projections extending radially from the catheter body. The effective O.D. of the wing plane can exceed the original O.D. of the fully inflated balloon. The presence of these wings makes it difficult to withdraw the catheter into its associated guide catheter and, additionally, may dislodge the otherwise secured stent graft during balloon withdrawal. U.S. Pat. No. 5,037,392 addresses this problem.
Accordingly, it is principal purpose of the present invention to provide an improved stent delivery catheter for use with relatively large diameter (5-50 mm) stents which can be inflated to a sufficiently high pressure to expand stents of this size without exceeding the burst strength of the balloon and which can be deflated without significant winging.
It has been previously established that the longer a balloon is inflated against a stenosis the better the patency result. However, it is also known that the longer downstream tissues are deprived of blood the more severe the resultant ischemia. During procedures involving stenosis and aneurisms in the aorta, for example, it is necessary to allow large volumes of blood to continue to pass beyond the worksite to the lower abdomen and into the legs. Failure to do so results not only in deprivation of blood to the lower extremities but also in a pressure build-up which when relieved (as in during withdrawal of the apparatus) can and has washed the stent graft, which had just been carefully placed, downstream and out of the physician's control, posing a risk to the patient, and further lengthening the procedure while the physician attempts to reposition the device.
Another problem that currently exists is the blockage of air into the lungs while balloon expanding a stent in the trachea, the right or the left bronchus.
Depending on the complexity and duration of the procedure, these aforementioned blockages of blood and air present substantially undesirable risks associated with much of the existing art currently in use to perform these types of interventions.
There are several inventions currently available which have attempted to address the need for perfusion of bodily media beyond the lesion site by bundling several balloons together however the result is only partially successful. Their limitations lie in the fact that perfusion is accomplished only because the bundled balloons create a "default orifice" between the junction of the outside radiuses of the circular balloons. These "default orifices" are relatively small and substantially restrict the volume of media which could pass through them. Furthermore, these "default orifices" being small could become clogged, completely stopping media passage altogether.
The present invention allows significantly larger volumes of media to pass beyond the lesion by deliberately forming the balloons into pie-shaped wedges which when assembled and connected to a fluid source can be selectively inflated or deflated either individually, simultaneously or in alternating groups. The concept of simultaneous inflation and deflation of alternating balloon members allows anchoring and expansion of the graft or stent while simultaneously allowing large quantities of blood or other media to pass.
There are conceivably other uses for a large diameter, high pressure, alternating cyclic expander member than so far mentioned. Conceivably, the inflation and deflation of alternating balloons could be cycled to match the pulsing of blood or the rhythm of breathing. One use may be as an interventional pump if there were a need to pump a dislodged device or mass of a biological nature either up or down stream.
If the diameter of the alternating balloons was varied between large and small, another use of the concept of separate balloon group inflation could be to expand two different stent graft diameters in different locations without withdrawal and exchange for another balloon size. In this scenario, it may be necessary to rotate the device such that all areas of the stent, graft, stenosis, etc. are uniformly dilated since only alternating balloons have the same effective diameter.